The present invention relates to the synthesis of highly active ruthenium or osmium carbene metathesis catalysts. To the synthetic organic or polymer chemist, simple methods for forming carbon-carbon bonds are extremely important and valuable tools. One method of C--C bond formation that has proved particularly useful is transition-metal catalyzed olefin metathesis. The past two decades of intensive research effort has recently culminated in the discovery of well defined ruthenium and osmium carbene complex catalysts that are highly metathesis active and stable in the presence of a variety of functional groups.
These ruthenium and osmium carbene complexes have been described in U.S. Pat. Nos. 5,312,940 and 5,342,909 and U.S. patent applications Ser. Nos. 08/708,057, 08/282,827 and 08/693,789, all of which are incorporated herein by reference. The ruthenium and osmium carbene complexes disclosed in these patents and applications all possess metal centers that are formally in the +2 oxidation state, have an electron count of 16, and are penta-coordinated. These catalysts are of the general formula ##STR2## where M is ruthenium or osmium, X and X.sup.1 are anionic ligands, and L and L.sup.1 are neutral electron donors and R and R' are specific substituents that will be described in more detail below.
U.S. Pat. Nos. 5,312,940 and 5,342,909 disclose specific vinyl alkylidene ruthenium and osmium complexes in which the neutral electron donor ligands L and L.sup.1 are triphenyl phosphines or diphenylmethyl phosphines. As disclosed in the patents, the catalysts are useful in catalyzing the ring opening metathesis polymerization ("ROMP") of strained olefins. U.S. patent applications Ser. Nos. 08/708,057 and 08/282,827 disclose specific vinyl alkylidene ruthenium and osmium complexes in which the neutral electron donor ligands L and L.sup.1 are phosphines with at least one secondary-alkyl or cycloalkyl substituent. These secondary-alkyl phosphine catalysts are more metathesis active than the corresponding triphenyl phosphine catalysts and may be used to catalyze a variety of metathesis reactions involving acyclic and unstrained cyclic olefins. U.S. patent application Ser. No. 08/693,789 discloses specific non-vinyl alkylidene complexes that are more metathesis active than their vinyl alkylidene counterparts. The preferred catalyst disclosed in this application are benzylidene ruthenium and osmium carbene compounds.
As disclosed by U.S. Pat. Nos. 5,312,940 and 5,342,909, vinyl alkylidene catalysts may be synthesized by a variety of methods including the reaction of ruthenium or osmium compounds with cyclopropenes or phosphoranes, and neutral or anionic ligand exchange. Of these previous methods, the preferred method of making the catalysts is via the reaction of a substituted cyclopropene with a ruthenium or osmium dihalide. Unfortunately, this method is limited to the synthesis of vinyl alkylidene catalysts (i.e., catalysts in which R is hydrogen and R.sup.1 is a substituted vinyl group) and cannot be used to directly synthesize the secondary-alkyl phosphine catalysts disclosed in the Ser. Nos. 08/282,826 and 08/282,827 applications. The synthesis of these secondary-alkyl phosphine catalysts further requires reacting the triphenyl phosphine catalysts produced from the cyclopropene reaction with secondary-alkyl phosphines in a ligand exchange reaction.
In part to overcome the fact that the cyclopropenes are not readily available and are generally limited to the synthesis of vinyl alkylidene catalysts, U.S. patent application Ser. No. 08/693,789 discloses a method for synthesizing alkylidene complex catalysts via the reaction of substituted diazoalkanes with ruthenium dihalides. The synthetic procedures disclosed in this application can be used to make non-vinyl alkylidene complex catalysts which are more metathesis active than their corresponding vinyl alkylidene counterparts. As in the cyclopropene based methods, the secondary-alkyl phosphine catalysts cannot be synthesized directly from the reaction of ruthenium dihalide and diazoalkanes. Instead, the secondary-alkyl phosphine catalysts must be synthesized by ligand exchange. Although the use of diazo starting materials greatly broadened the range of ruthenium and osmium carbene catalysts that could be synthesized, the danger of handling diazocompounds on a large scale severely restricts the commercial and laboratory utility of this method. In addition, the diazo method requires the synthesis to be conducted at low temperature (about -80.degree. C. to -50.degree. C.) and requires the use of considerable solvent in the final purification of the catalyst. As with the cyclopropene synthesis method, the secondary-alkyl phosphine catalysts must be synthesized using a multi-step ligand exchange procedure which may be time consuming and expensive and may result in lower product yields.
In both the cyclopropene and diazo synthesis methods the secondary-alkyl phosphine catalysts must be synthesized using a multi-step, ligand exchange procedure. Since the secondary-alkyl phosphine catalysts are more metathesis active than the triphenyl phosphine catalysts and therefore may have wider commercial utility, the necessity of a multi-step synthesis in these cases can be a severe limitation.
Although the previous methods have been adequate to make reasonable quantities of the ruthenium and osmium carbene catalysts, as the number of scientific and commercial applications of these catalysts continues to increase, a need exists for simple, safe, and inexpensive methods of synthesizing these compounds to fully exploit their potential.